The present invention relates to subscription television signal scrambling and descrambling systems and methods.
At the present time a number of scrambling-descrambling methods are used to prevent unauthorized viewing of television signals by non-subscribers. For example, the television signal is broadcast by cable, over-the-air microwave system, over-the-air VHF/UHF, or communication satellite, and certain, or all, of the programs on a channel are scrambled. The viewer generally pays a monthly fee and obtains a descrambler box ("decoder box") which is connected between the cable, or antenna, and the television receiving set ("TV set").
In addition to the sample monthly bill for scrambled channels, such as the "HBO" (Home Box Office) channel, there is also available in some areas other types of pay programs. In "Pay-Per-View" ("PPV") the viewer only pays for the pay programs he selects, for example, a boxing, tennis, or other sporting event. In "Impulse Purchasing" the viewer may select the pay-per-view program at the last moment or even after the program has started.
The presently commercially available scrambling-descrambling systems have two basic problems. First, they are not secure against "piracy", which is the use of unauthorized decoder boxes. It is relatively easy, and common, to buy another decoder box, replace one or more of its components, receive scrambled programs and descramble them without paying fees to the broadcaster. Secondly, some systems are not adapted for pay-per-view or impulse purchasing, which is limiting to the marketing of programs.
U.S. Pat. No. 4,115,807 to Pires, incorporated by reference herein, describes a scrambling-descrambling system including a program identification code unique to a program (block of material). If the viewer selects a program, its program identification code is stored, in the memory of the decoder box, for billing by periodic polling on a telephone line by a central computer. In addition, if the subscriber has paid his bill, the central computer supplies new program code numbers for the next month's program which enables the decoder box to continue its descrambling operation. The new program code number is compared to a code which is inserted in the vertical interval of the video signal, to enable the descrambling circuitry. The scrambling-descrambling system used is the video inversion system of Teleglobe's Horowitz U.S. Pat. No. 3,824,232, incorporated by reference herein. Also see U.S. Pat. Nos. 4,528,589; 4,225,884; 4,126,762 and 4,163,254.
In the previous above-mentioned patents, there is no broadcast communication to the decoder box which readies it to receive a telephone call from the central computer. A person may duplicate the information, including the descrambling code, from a legal decoder box and sell it to those with unauthorized boxes.
In Northern Telecom U.S. Pat. No. 4,388,643 broadcast codes are used along with a subscriber number code stored in the decoder box; and a polling central computer is used for billing. The central computer reads out the subscriber's decoder box number ("SN") and a new set of codes ("ICK" and "DK") are furnished to the decoder box. As in other systems, the codes supplied to one legal decoder box may be appropriated and given to those with illegal decoder boxes.
U.S. Pat. No. 4,494,142 to Blonder-Tongue discloses broadcasting a special code addressed only to those decoder boxes having a preset unique address. U.S. Pat. No. 4,325,078 shows the use of a one-time usage magnetic program card which is inserted by the viewer into a card reader to enable the descrambling converter.
In addition to the video inversion system of the Teleglobe-Horowitz patents, various other scrambling-descrambling systems have been patented, all of which are applicable to the security system of the present invention. For example, in M/A Com Linkabit U.S. Pat. No. 4,563,702 video information lines are stored in memory and their order scrambled. Another scrambling-descrambling system is shown in U.S. Pat. No. 4,614,970 to U.S. Computer Systems.